Vascularisation, including angiogenesis, is the fundamental process by which new blood vessels are formed and is essential to a variety of normal body activities, such as reproduction, development and wound repair in adult.
Angiogenesis requires the functional activity of a wide variety of molecules, including growth factors (VEGF, FGF), extracellular matrix proteins, adhesion receptors and proteolytic enzymes. During angiogenesis, the coordinated regulation of these proteins leads to endothelial cell proliferation, matrix remodeling, cellular migration/invasion, and eventually, differentiation. For instance, recent studies reported that angiogenesis depends on specific endothelial cell adhesive events mediated by integrin αvβ3 (Brooks, P C, et al., Science, 264: 569-571 (1994); Brooks, P. C, et al. Cell, 79: 1157-1164 (1994); Friedlander, M, et al., Science 270: 1500-1502 (1995)). Thus, the physiological control of angiogenesis is dependent on the balance of activators and inhibitors present within the vascular microenvironment.
Although angiogenesis is a highly regulated process under normal conditions, many diseases are driven by persistent unregulated angiogenesis. These clinical manifestations associated with angiogenesis are referred to as angiogenic diseases.
For instance, certain existing conditions such as arthritis, newly formed capillary blood vessels invade the joints and destroy cartilage. In diabetes, new capillaries formed in the retina invade the vitreous, bleed, and cause blindness.
Growth and metastasis of solid tumors are also angiogenic diseases (Folkman, J., Cancer Research, 46: 467-473 (1986)). It has been shown, for example, that tumors must obtain their own blood supply and do so by inducing the growth of new capillary blood vessels. Once these new blood vessels become embedded in the tumor, they provide a means for tumor cells to enter the circulation and metastasize to distant sites, such as liver, lung or bone (Weidner, N., et al., The New England Journal of Medicine, 324(1): 1-8 (1991)).
Because angiogenic diseases impact a large number of people each year compositions and treatment methods for treating these diseases are highly desirable.
From now on it is clear that blocking angiogenesis may be highly efficient treating angiogenic diseases. For example, there is great evidences supporting the contention that blocking tumor neovascularization can inhibit tumor growth in various animal models, and human clinical data is beginning to support this contention as well (Varner, J. A., Brooks, P. C., and Cheresh, D. A. (1995) Cell Adh. Commun. 3, 367-374). Therefore several angiogenesis inhibitors are currently under development for use in treating angiogenic diseases.
In contrast, angiogenesis has also been the focus of intense interest since this process may be exploited to therapeutic advantage. Stimulation of angiogenesis may useful in the healing of wounds, vascularizing of skin grafts, and the enhancement of collateral circulation where there has been vascular occlusion, stenosis or ischemia. Actually, ischemia caused by acute injury or arterial occlusion sometimes results in loss of fingers, functional disorders, or serious diseases that lead to death. Due to changes of social environment and the arrival of an aging society, ischemic heart diseases such as acute myocardial infarction and severe angina pectoris, in particular have increased rapidly, and now account for the majority of lifestyle-related diseases. Therefore, there is an intense interest in the art for providing tools able to stimulate angiogenesis.
Dystrophin is a submembraneous protein, and represents the core of a protein complex that connects the cytoskeleton of the muscle fiber to the surrounding extracellular matrix through the cell membrane. Dystrophin has the longest gene known to date, measuring 2.5 megabases (0.1% of the human genome). Its gene's locus is Xp21 and has 79 exons, produces an mRNA of 14.6 kilobases and a protein of over 3500 amino acid residues.
Dystrophin is a multidomain protein consisting of an N-terminal actin-binding domain, a rod domain containing 24 spectrin-like repeats, a cysteine-rich domain, and a C-terminal domain. The two latter domains bind to proteins of the DAP (dystrophin associated protein) complex and the syntrophins. Alternative splicing of some of the 79 exons of the dystrophin gene produces several dystrophin iso forms, ranging from 71 kDa to the full-length 427 kDa. At least 7 independent promoters drive the transcription of 7 different dystrophin products (i.e. Dp260, Dp140, Dp116, Dp71 . . . ) that are expressed in a cell-specific manner.
Recently, Dalloz et al. (2003) have investigated the potential role of Dp71, the most abundant C-terminal dystrophin gene product, in retina. They showed that Dp71 is expressed by Müller Glial Cells (MGCs) which form together with astrocytes the glia limitans of retinal vessels and induce barrier properties in them. However no role in angiogenesis has been yet suspected.